Two new genera in the Arthoniales are described from the Pacific Islands. Glyphopsis, with the new species G. aurantiodisca from New Caledonia is characterized by a thallus containing divaricatic acid and zeorin and sessile grouped ascomata with bright orange discs and raised lecanorine margins, and the ascospores hyaline and muriform. Gossypiothallon, with the new species G. appendisporum from the Solomon Islands is characterized by a byssoid thallus containing zeorin and pedicillate, simple ascomata with pale pink discs, without differentiated margins and hyaline, bacillar, 3-septate ascospores with two polar, usually curved gelatinous appendages. Eight further corticolous crustose lichens are described from either New Caledonia or the Solomon Islands. Byssoloma xanthonicum is characterized by a thallus containing norstictic acid and lichexanthone and 3-septate ascospores. Cliostomum ovocarpum has orange yellow, convex apothecia and 1-septate ascospores. Crocynia minutiloba has palmately branched lobes on a thick whitish byssoid hypothallus and flat lecideoid apothecia. Megalotremis dolabarata has superficial cylindrical grey pycnidia and simple ellipsoid conidia. Pyrenula filiformis has a thallus with pseudocyphellae covering most part of the ascomata and 11–17-septate, slender fusiform to slightly clavate ascospores. Pyrenula mastigophora has 5-septate ascospores with an up to 25 µm long tail at the lower end. Pyrenula spissitunicata has a thallus with lichexanthone, fused ascomata with common ostioles covered by thallus and ascospores resembling a Pyrgillus. The lichenicolous fungus Pyrenidium coccineum (parasitic on Siphula decumbens) has red ascomata which stain herbarium boxes blue.